3DFlex: A flexible system for total visual inspection of bumped devices

Most bumped packages (WL-CSPs, BGAs, etc) undergo the necessary 3D visual inspection in tray-scan machines or at the wafer level, or sometimes there is no 3D inspection, relying on process stability and correlation with 2D inspection alone. This means the device are further manipulated before they are placed into tape, and there is the risk of them being actually damaged. This risk is more important as bumps become smaller. To address this problem Ismeca has developped 3DFlex, a single-station vision module for touchless 3D and 2D collocated inspection of bumped devices (bumped die, μBGA) under turret on Ismeca field-bus machines (NX32W, NX16), running on our novel NativeNET vision system. The system, capable of inspecting bumped-dies and BGAs from 0.8x0.8 mm up to 6x6 mm, comprises 2D inspection (bump presence, bump diameter, bump pitch, surface inspection) and 3D inspection (bump standoff, bump volume, coplanarity) in a single station. This module is intended to be placed on the handler right before the taping module, so that devices in the tape are guaranteed not to be damaged between 3D inspection and taping. The 3D measurement is based on projection moire phase shift interferometry techniques, allowing for full-image, fast, and precise topographic measurement. An advantage of this system is that it is software configurable, thus eliminating setup time when changing between parts and requiring no tooling. Additionally, contrarily to other 3D techniques such as stereo, moire interferometry creates a 3D-measurement at every image pixel -except in shadow areas- providing full part topography and allowing to tackle very complex part geometries: studs, columns, mix of balls and studs, parts with balls of different heights, etc. During production the system captures up to 2 images for 2D inspection (typically one to inspect the package, another to inspect the balls) and 3 images for the 3D inspection that are then processed to create a range image from which ball standoff and coplanarity can be measured. Process time is such that a throughput of 18'000-24'000 units/h can be reached (depending on part size). Images are captured with a VGA camera (640x480 pixels), leading to a 2D-resolution of 14 μm/pixel and a software-configurable 3D-resolution down to 0.4 μm/step. Experimental measures have shown bump height/standoff repeatability to be 7 μm (3σ) and correspondingly ball diameter and ball offset repeatability to be 5 μm (3σ).